1. Field of the Invention
The present invention generally relates to method and apparatus for recording digital data streams, and more particularly, but not by way of limitation, to method and apparatus for recording transport stream units of a digital data stream in stream object units of a recording medium having sectors of a fixed size.
2. Description of the Related Art
In the conventional analog television broadcast, video signals are transmitted over the air or through cables after being AM or FM modulated. With the recent advance of digital technologies such as digital image compression or digital modulation/demodulation, standardization for digital television broadcast is in rapid progress. Based upon the Moving Picture Experts Group (MPEG) format, satellite and cable broadcast industry also moves towards the digital broadcast.
The digital broadcast offers several advantages that its analog counterpart cannot provide. For example, the digital broadcast is capable of providing services with far more improved video/audio quality, transmitting several different programs within a fixed bandwidth, and offering enhanced compatibility with digital communication media or digital storage media.
In the digital broadcast, a plurality of programs encoded based upon the MPEG format are multiplexed into a single transport stream before transmitted. The transmitted transport stream is received by a set top box at the receiver and demultiplexed into original programs. If a program is chosen from among the demultiplexed programs, the chosen program is decoded by a decoder in the set top box and original audio and video signals are retrieved. The retrieved audio and video signals can be presented by an A/V output apparatus such as a TV.
FIG. 1 depicts a block diagram of a general digital data stream recording apparatus comprising a set top box 100, a communication interface (IEEE-1394), and a streamer 200. The set top box 100 receives transport streams encoded by system encoders and broadcast by a plurality of broadcasting stations and demultiplexes the received transport streams. After a system decoder 120 decodes the transport stream of a program tuned by a tuning unit 110, a control unit 140 outputs the decoded transport stream to an A/V output device such as a TV set for presentation. The set top box 100 may transmit a program chosen by a user to the streamer 200 through the IEEE-1394 interface so that the transmitted program is recorded on a recording medium 230 such as a digital video disk by the streamer 200.
Requested by a user, the set top box 100 may receive a program retrieved from the recording medium 230 by the streamer 200 through the IEEE-1394 communication interface so that the received program can be presented on a TV set after being decoded by the decoder 120.
For recording the received digital broadcast signals on a recording medium, it is necessary to develop schemes for organizing the received digital data streams on the recording medium as groups of stream object units and creating management information for the stream object units. However, no international standard for such schemes is available yet and thus various methods have been proposed by relevant developers.
A conventional method for creating stream object units will be explained with reference to accompanying drawings.
FIG. 2 shows the syntax of several digital data stream recording units. A stream object (SOB), which is a single recorded program, comprises a plurality of stream object units and a stream object unit (SOBU) comprises a plurality of sectors. A sector further comprises a plurality of transport stream packets (TSPs) and header information (HDRS) regarding the transport stream packets.
To be more specific with figures, the size of a transport stream packet is 192 bytes, the size of the header information (HDRS) is 100 bytes, and the size of a sector is 2048 bytes. A sector of 2048 bytes comprises a 100-byte header information (HDRS), 10 192-byte transport stream packets, and a 28-byte padding area padded with null data. The 100-byte header information (HDRS) further comprises a sector header for identifying the sector and several headers. A transport stream packet comprises a 4-byte time stamp representing the packet arrival time and a 188-byte application packet.
FIG. 3 is a detailed view of the application header recorded in the header information area (HDRS). The application header comprises several fields representing the header format version (VERSION), the identification code of the data stream (APPLICATION_ID), the maximum bit transfer rate of the data stream (MAX_BITRATE), the buffer size (SMOOTH_BUF_SZ), the reference clock frequency for packet arrival/transmission (TS_REF_CL_FREQ), the length of a transport stream packet (AP_PKT_LEN), the length of a transport packet arrival time (TS_LEN), the number of transport stream packets (AP_PKT_Ns), the first transport stream packet of the data stream (START_OF_STR), and the last transport stream packet of the data stream (END_OF_STR). The number of 188 representing that the size of a transport stream packet except the time stamp is 188 bytes is recorded in 2 bytes in the field of AP_PKT_LEN and the number of 10 representing that a sector comprises 10 transport stream packets is recorded in 1 byte in the field of AP_PKT_Ns.
According to the conventional method for recording digital data streams, a predetermined number of sectors are grouped into a stream object unit (SOBU) and a sector comprises 100-byte header information (HDRS), 10 192-byte transport stream packets including time stamps, and 28-byte padding area, as shown in FIG. 4,
As a result, a stream object unit (SOBU) comprising 32 sectors contains 32 28-byte padding areas and therefore the size of padding areas contained in a stream object unit (SOBU) amounts to 886 bytes. As the padding area contains no useful information, such a recording method severely impairs the recording efficiency of the recording medium.